Area Forecast Discussion
Issued by NWS Wilmington, NC
FXUS62 KILM 291142
Area Forecast Discussion
National Weather Service Wilmington NC
742 AM EDT Thu Sep 29 2016
A cold front approaching from the west will slow down on Friday and
linger near or along the Carolina coast through this weekend. High
pressure will build in behind the front through early next week.
.NEAR TERM /THROUGH TONIGHT/...
As of 600 AM Thursday...Have upped the POPs across the
northern portions of the FA to account for the persistent
convection and also to account for its very slow movement
eastward with time. The QPF has been updated and increased across
the aforementioned areas that will see POPs raised.
As of 330 am Thursday...SPC has a good portion of the ILM
CWA...mainly away from the immediate coast...in a marginal risk
today into this evening.
The cutoff low is progged to drop to central Kentucky by Friday
morning. Models indicate that this will be its furthest southern
push. Dynamics associated with mid-level vorts or s/w trofs,
interacting with the sfc cold front now across the central
Carolinas, and rotating around this upper low further aid the
development and persistence of convection today. Persistence,
meaning even after the days insolation has ceased the convection
will continue. This illustrated well by the convection that has
persisted across central NC during these pre-dawn Thu hours. In
general, have peaked POPs at 50 percent. But, depending on where
the current convection continues at xmit time, may go hier to
likely then drop it back down later this morning.
POPs have been continued along the immediate ILM CWA coast during
the pre-dawn Fri hrs due to convection aided by an upper s/w trof
tracking nearly due north around the periphery of the cutoff low.
The nocturnal development of convection over the Atl waters this
time of the year will also play a part.
As for temps, the European and NAM MOS Guidance, both have been
doing well with daytime highs based on the latest verification
stats for the local area for the past several days. For night time
Lows, the NAM Mos alone, is verifying the best.
.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
As of 345 AM Thursday...To no surprise, the cutoff upper low and
mid-level vorts, like spokes on a bicycle tire, rotating around
it will be the driver of the sensible weather across the ILM CWA
this period. The good news, models have this cutoff/closed low
slowly opening up and lifting northward by the end of this period
as a result of the strong westerlies now able to move this upper
feature. At the sfc, the cold front will slowly make some progress
to the coast on Friday and on Saturday it basically stalls either
along the immediate coast or just offshore due to it becoming
parallel with the flow aloft. Therefore POPs will be confined
along the eastern 1/3rd of the ILM CWA and the adjacent Atlantic
waters thruout this period. The dry slot or tongue will affect
mainly the western 2/3 of the ILM CWA helping to eliminate POPs
in that area. Could see hier POPs during the pre- dawn hrs along
the immediate coast during the pre- dawn Sat and Sun hours due to
the combined nocturnal development over the waters and any mid-
level vorts having either rotated around the cutoff low or picked
up off the Florida west coast or the northern Bahamas. Max/Min
temps to remain above normal, 1 to 2 categories, thruout this
.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
As of 3 AM Thursday...Large upper low finally lifting out to the
northeast early in the period. In its wake will be a weak pressure
gradient and a dissipating frontal boundary just offshore. A few
showers along this front may affect coastal locales but suspect that
most areas stay rain-free and seasonable. As the upper low begins to
interact with troughiness east of Canada rising surface pressures
advect into the eastern U.S. Tuesday and Wednesday. Should this flow
be NE then some lower dewpoints may creep into the Carolinas but
current progs show more ENE and likely preclude that. Building
heights aloft argue for not much in the way of meaningful precip
though a few sprinkles tough to rule out in the onshore low level
flow. This gradient could become pinched by Matthew and it may
become breezy locally by Wednesday if the quick GFS is correct.
.AVIATION /12Z THURSDAY THROUGH MONDAY/...
As of 12Z...A surface boundary is noted N of KILM to between
KFLO/KLBT. Showers/thunderstorms are sct S of the boundary with the
best coverage N of the boundary.
Showers appear likely at all terminals into the afternoon, with
VCTS this morning KLBT and this afternoon at the coastal
terminals. MVFR most likely N of the boundary at KLBT this
morning, with VFR/TEMPO MVFR/IFR elsewhere associated with
precipitation. IFR is too brief to mention in TAFS. Could be a
decrease in coverage as the day progresses and some drier air
intrudes. MVFR should become less likely at KLBT EARLY afternoon
as the surface boundary shifts N. There is a chance showers could
re-develop KLBT-KFLO around midnight Z.
EXTENDED OUTLOOK...Primarily VFR. Isolated to scattered afternoon
showers through much the period, although limited in strength and
coverage due to dry air aloft.
NEAR TERM /THROUGH TONIGHT/...
As of 605 AM Thursday...The sfc cold front to remain inland from
the coast during this period. That means a southerly wind will
continue across the local waters thruout this period. The sfc pg
to remain semi-tightened ahead of the cold front and should
produce 10 to 15 kt wind speeds...and could see occasional gusts
up to 20 kt, especially during the overnight period. Significant
seas will run a solid 3 foot. The spectral density charts indicate
that a pseudo easterly swell at 7 second periods, with an
occasional ese swell at 10 second periods, will both dominate the
seas spectrum. Wind driven waves will mesh on top of this e to ese
ground swell. Convection this morning will move across the local
waters, mainly between Little River Inlet and Surf City.
SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
As of 400 AM Thursday...The movement of the cold front at a
snail`s pace will push it to the coast late Friday and possibly
either across the coastal waters or just offshore from Carolina
coastlines. The sfc pressure pattern will result in a S to SW wind
direction thruout this period. The sfc pg will remain
semi-tightened east of the cold front, with 10 to 15 kt speeds,
and somewhat relaxed in the vicinity of the cold front, with 10 kt
or less speeds. Significant seas to continue at 2 to 3 ft thruout
this period. The ese ground swell at 7 to 9 second periods will
mainly dominate the seas with local wind driven waves at 3 to 4
seconds on top. Expect convection thruout this period, with the
pre-dawn hrs thru daytime morning hrs of each day exhibiting the
hier pops during this period.
LONG TERM/SUNDAY THROUGH MONDAY/...
As of 3 AM Thursday...Weakening front along the coast Sunday will
keep winds very light though there is some uncertainty regarding
direction-though primarily onshore. Small wind chop combine w ESE
swell for a 2 to 3 ft dominant wave height. No significant changes
noted heading into Monday.